1. Viewing Systems for Use with the Human Eye
A variety of viewing systems for use with the human eye are known. They fall into two categories: 1) those which are normally fixed during viewing with respect to the object such as telescopes and microscopes ("fixed systems"), and 2) those which are normally moved during viewing with respect to the object such as eyeglasses, loupes, monoculars, and binoculars ("movable systems"). The present invention relates to movable systems and, in particular, to monoculars and binoculars. To simplify the presentation, the following discussion uses the term "binoculars." As so used, the term is intended to include both binoculars and monoculars.
To understand the benefits of the invention it is necessary to understand how a person observes an event without binoculars, i.e., unaided by a viewing system. The first step, in general, involves noticing the movement of the image of an object on the retina in the low resolution, peripheral vision. The extent over which such movement can be observed is the eye's "unaided static field of view". Next, the eye is moved (scanned) to follow or observe the object in greater detail, i.e., at high resolution, by aligning the eye's fovea with the object. The extent over which the eye can move to follow the object is the eye's "unaided dynamic field of view". Finally, the head is moved so that the eye is as straight ahead as possible with respect to the head.
For the purposes of the following discussion, these two fields of view of the eye, i.e., the eye's unaided static and dynamic fields of view, need to be distinguished from the eye's "aided static field of view" and "aided dynamic field of view" which are the fields of view achieved for a static and scanning eye, respectively, with binoculars held at a fixed position relative to the eye. These aided fields of view are defined and discussed in more detail below. As also discussed below, it should be noted that the eye's aided static field of view is the same as what is commonly referred to as a binoculars' "field of view" when transformed to image space.
2. Binocular Technology
Historically, designers of binoculars have concentrated on maximizing the eye's higher resolution aided dynamic field of view at the expense of the eye's lower resolution aided static field of view. In particular, designers have assumed that the user rotates (scans) his or her eyes to follow an object and then after seeing the image start to disappear because the exit pupil of the binoculars is not coincident with the entrance pupil of the rotated eye, moves the binoculars thereby placing the two pupils in coincidence.
As a result, the image has been corrected over the entire "field of view" and a field stop has been used to delimit the "field of view" in order to ensure that the user has a corrected image throughout the eye's aided dynamic field of view. In order to provide a hand held instrument at reasonable cost, this has meant that the eye's aided static field of view has been limited, i.e., less than about 30.degree. semi-field of view (SFOV) and in many cases less than about 20.degree. SFOV.
Recently, various companies have offered "wide angle" binoculars. These binoculars are reported to have semi "fields of view" in object space which when transformed to image space, assuming f-.theta. distortion correction, correspond to semi "fields of view" in image space of around 33.degree. . Although they represent some improvement over prior binoculars, as discussed below, these "wide angle" binoculars have still not satisfied the need for binoculars which truly deal with the fundamental difference between the eye's aided static and dynamic fields of view.